1. Field of the Invention
The present invention relates to a shift drum drive system for a transmission including a gear speed change mechanism provided in the course of a power transmission path for transmitting rotational power of a crankshaft to a drive wheel. The gear speed change mechanism is contained in a crankcase rotatably bearing the crankshaft. A shift drum constitutes a part of the gear speed change mechanism and is turnably borne by the crankcase. A speed change controller is configured to drive the shift drum to turn so as to cause the gear speed change mechanism to perform a speed change operation. The speed change controller includes a drive means for producing rotational power and a power transmission device configured to transmit the rotational power of the drive means to the shift drum, with the drive means and at least a part of said power transmission device being disposed on a lateral side of the crankcase on the side of one end in the axial direction of the shift drum.
2. Description of Background Art
A shift drum drive mechanism for a transmission is known wherein a shift drum is driven to turn by the power produced by a drive means and a speed change operation is thereby automatically performed. See, for example, Japanese Patent Laid-open No. Hei 5-39865.
However, in the system disclosed in Japanese Patent Laid-open No. Hei 5-39865, the shift drum and the drive means are disposed at mutually spaced positions as viewed along the axial direction of the shift drum, which leads to an enlarged engine size.